TMS zl Management and Configuration Guide ST.1.1.100226

4-51
Firewall
User Authentication
Table 4-8. Advantages and Disadvantages of CHAP
MS-CHAP. The TMS zl Module supports MS-CHAPv2 for RADIUS authenti-
cation, which is incompatible with, though similar to, MS-CHAPv1.
MS-CHAPv2 is compatible with both Windows XP and Windows Vista, the two
most current Microsoft operating systems.
MS-CHAP works in the same way as CHAP, with a few exceptions:
■ The RADIUS, or authenticator, does not need to store a plaintext version
of the secret, so the secret can be irreversibly encrypted.
■ It includes a Change-Password packet that allows the client to change the
password on the account that’s being authenticated.
■ It always defines a reason for failure in the Access-Reject packet.
PAP. PAP uses a two-way handshake to authenticate uses. The CHAP authen-
tication process is shown in detail below.
Figure 4-31. PAP Handshake
The PAP handshake process is as follows:
1. The client sends a request to the NAS. The NAS translates the packet and
forwards it to the RADIUS server. This packet includes only a username
and password.
Advantages Disadvantages
• Prevents playback attacks by
incrementally changing the identifier and
challenge values.
• Both the client and the server must know
the secret, but the secret is never sent
over the line.
• The shared secret must be in plain text, so
you cannot use irreversibly encrypted
passwords.